Body Tissues

TISSUES– Groups of cells with similar structure and function

– Four primary types

• Epithelial tissue (epithelium)

• Connective tissue

• Muscle tissue

• Nervous tissue

Epithelial Tissues• Locations

– Body coverings

– Body linings

– Glandular tissue

• Functions

– Protection

– Absorption

– Filtration

– Secretion

• Cells fit closely together and often form sheets

• The apical surface is the free surface of the tissue

• The lower surface of the epithelium rests on a basement membrane

• Avascular (no blood supply)

• Regenerate easily if well nourished

Classification of Epithelia• Number of cell layers

– Simple—one layer

– Stratified—more than one layer

• Shape of cells

– Squamous• flattened

– Cuboidal• cube-shaped

– Columnar• column-like

Simple Epithelia• Simple squamous

– Single layer of flat cells

– Usually forms membranes

• Lines body cavities

• Lines lungs and capillaries

• Simple cuboidal

– Single layer of cube-like cells

– Common in glands and their ducts

– Forms walls of kidney tubules

– Covers the ovaries

• Simple columnar

– Single layer of tall cells

– Often includes mucus-producing goblet cells

– Lines digestive tract

Stratified Epithelia• Stratified squamous

– Cells at the apical surface are flattened

– Found as a protective covering where friction is common

– Locations• Skin

• Mouth

• Esophagus

• Stratified cuboidal—two layers of cuboidal cells

• Stratified columnar—surface cells are columnar, cells underneath vary in size and shape

• Stratified cuboidal and columnar

– Rare in human body

– Found mainly in ducts of large glands

• Pseudostratified columnar

– Single layer, but some cells are shorter than others

– Often looks like a double layer of cells

– Sometimes ciliated, such as in the respiratory tract

– May function in absorption or secretion

• Transitional epithelium

– Shape of cells depends upon the amount of stretching

– Lines organs of the urinary system

Glandular Epithelium• Gland

– One or more cells responsible for secreting a particular product

• Two major gland types

– Endocrine gland

• Ductless since secretions diffuse into blood vessels

• All secretions are hormones

– Exocrine gland

• Secretions empty through ducts to the epithelial surface

• Include sweat and oil glands

Connective Tissue

• Found everywhere in the body

• Includes the most abundant and widely distributed tissues

• Functions

– Binds body tissues together

– Supports the body

– Provides protection

• Extracellular matrix

– Non-living material that surrounds living cells

Connective Tissue Types

• Bone (osseous tissue)

– Composed of

• Bone cells in lacunae (cavities)

• Hard matrix of calcium salts

• Large numbers of collagen fibers

– Used to protect and support the body

• Hyaline cartilage

– Most common type of cartilage

– Composed of

• Abundant collagen fibers

• Rubbery matrix

– Locations

• Larynx

• Entire fetal skeleton prior to birth

• Elastic cartilage– Provides elasticity

– Location• Supports the external ear

• Fibrocartilage– Highly compressible

– Location• Forms cushion-like discs between vertebrae

• Dense connective tissue (dense fibrous tissue)

– Main matrix element is collagen fiber

– Fibroblasts are cells that make fibers

– Locations

• Tendons—attach skeletal muscle to bone

• Ligaments—attach bone to bone at joints

• Dermis—lower layers of the skin

• Loose connective tissue types

– Areolar tissue

• Most widely distributed connective tissue

• Soft, pliable tissue like “cobwebs”

• Functions as a packing tissue

• Contains all fiber types

• Can soak up excess fluid (causes edema)

– Adipose tissue

• Matrix is an areolar tissue in which fat globules predominate

• Many cells contain large lipid deposits

• Functions– Insulates the body

– Protects some organs

– Serves as a site of fuel storage

– Reticular connective tissue

• Delicate network of interwoven fibers

• Forms stroma (internal supporting network) of lymphoid organs

– Lymph nodes

– Spleen

– Bone marrow

• Blood (vascular tissue)

– Blood cells surrounded by fluid matrix called blood plasma

– Fibers are visible during clotting

– Functions as the transport vehicle for materials

Muscle Tissue

• Function is to produce movement

• Three types

– Skeletal muscle

– Cardiac muscle

– Smooth muscle

• Skeletal muscle

– Under voluntary control

– Contracts to pull on bones or skin

– Produces gross body movements or facial expressions

– Characteristics of skeletal muscle cells

• Striated

• Multinucleate (more than one nucleus)

• Long, cylindrical

• Cardiac muscle

– Under involuntary control

– Found only in the heart

– Function is to pump blood

– Characteristics of cardiac muscle cells

• Cells are attached to other cardiac muscle cells at intercalated disks

• Striated

• One nucleus per cell

• Smooth muscle

– Under involuntary muscle

– Found in walls of hollow organs such as stomach, uterus, and blood vessels

– Characteristics of smooth muscle cells

• No visible striations

• One nucleus per cell

• Spindle-shaped cells

Notice the similarities

Nervous Tissue

• Composed of neurons and nerve support cells

• Function is to send impulses to other areas of the body

– Irritability -Conductivity

Tissue Repair (Wound Healing)• Determination of method

– Type of tissue damaged

– Severity of the injury

A. Regeneration

– Replacement of destroyed tissue by the same kind of cells

B. Fibrosis

– Repair by dense (fibrous) connective tissue (scar tissue)

Events in Tissue Repair• Capillaries become very permeable

– Introduce clotting proteins

– A clot walls off the injured area

• Formation of granulation tissue

– Growth of new capillaries

– Rebuild collagen fibers

• Regeneration of surface epithelium

– Scab detaches

• Tissues that regenerate easily

– Epithelial tissue (skin and mucous membranes)

– Fibrous connective tissues and bone

• Tissues that regenerate poorly

– Skeletal muscle

• Tissues that are replaced largely with scar tissue

– Cardiac muscle

– Nervous tissue within the brain and spinal cord